An LCD utilizes liquid crystal molecules to control light transmissivity of each of pixel unit regions thereof. The liquid crystal molecules are driven according to external video signals received by the LCD. A conventional LCD generally employs a selected one of a frame inversion driving method, a line inversion driving method, a 1-line dot inversion driving method, and a 2-line dot inversion driving method to drive the liquid crystal molecules. Each of these driving methods can protect the liquid crystal molecules from decay or damage.
FIG. 7 is essentially an abbreviated circuit diagram of a conventional LCD. The LCD 100 includes a liquid crystal panel 10, a timing controller 101, a scanning circuit 102, a data circuit 103, and a common voltage generating circuit (not shown). The scanning circuit 102, the data circuit 103, and the common voltage generating circuit are configured for driving the liquid crystal panel 10.
The liquid crystal panel 10 includes a plurality of parallel scanning lines G1˜Gn, a plurality of parallel data lines D1˜Dm orthogonal to the scanning lines G1˜Gn, and a plurality of pixel units 130 cooperatively defined by the crossing scanning lines G1˜Gn and data lines D1˜Dm. The scanning lines G1˜Gn are electrically coupled to the scanning circuit 102, and the data lines D1˜Dm are electrically coupled to the data circuit 103.
Each pixel unit 130 includes a thin film transistor Qab (where a and b are natural numbers, 1≦a≦n, 1≦b≦m) and a liquid crystal capacitor Ccd (where c and d are natural numbers, 1≦c≦n, 1≦d≦m). The thin film transistor Qab is disposed near an intersection of a corresponding one of the scanning lines G1˜Gn and a corresponding one of the data lines D1˜Dm. A gate electrode of the thin film transistor Qab is electrically coupled to the corresponding one of the scanning lines G1˜Gn, and a source electrode of the thin film transistor Qab is electrically coupled to the corresponding one of the data lines D1˜Dm. Further, a drain electrode of the thin film transistor Qab is electrically coupled to the liquid crystal capacitor Ccd.
The scanning circuit 102 outputs a plurality of scanning signals to scan the plurality of scanning lines G1˜Gn successively. For example, when the scanning line G1 is scanned, the thin film transistors Q11˜Q1m are turned on simultaneously. Then the data circuit 103 outputs data signals to the liquid crystal capacitors C11˜C1m via the data lines D1˜Dm and corresponding thin film transistors Q11˜Q1m. The common voltage generating circuit outputs common voltages to the liquid crystal capacitors C11˜C1m. After all the scanning lines G1˜Gn have been scanned in a single frame period, the aggregation of light transmitting through the respective pixel units 130 constitutes the display of an image on the liquid crystal panel 10.
The data signals applied to each liquid crystal capacitor Ccd include positive polarity data signals (+) and negative polarity data signals (−). A value of each positive polarity data signal is greater than that of the common voltage, and a value of each negative polarity data signal is less than that of the common voltage. When an absolute value of a difference between the positive polarity data signal and the common voltage of any one pixel unit 130 is equal to an absolute value of a difference between the negative polarity data signal and the common voltage of any other pixel unit 130, the two pixel units 130 display picture elements having a same gray level.
FIG. 8 is a diagram illustrating a principle of the 1-line dot inversion driving method. In order to simplify the following explanation, FIG. 8 only shows a 4-by-4 sub-matrix of pixel units 130 of the liquid crystal panel 10. The other pixel units 130 of the liquid crystal panel 10 have a polarity arrangement similar to that shown in FIG. 8. The polarity of each pixel unit 130 in FIG. 8 is opposite to the polarity of every directly adjacent pixel unit 130, and the polarity of each pixel unit 130 is reversed once in every frame period. When a 1-line dot inversion test pattern as shown in FIG. 9 is applied to the liquid crystal panel 10, the pixel units 130 arranged along oblique lines in the sub-matrix are in dark states, and the other pixel units 130 in the sub-matrix are in bright states.
Referring to FIG. 10, this illustrates an operation principle of displaying the 1-line dot inversion test pattern of FIG. 9 on the LCD 100 using the 1-line dot inversion driving method. The pixel units 130 marked with circles all have positive polarities during an (n−1)th frame period, negative polarities during an nth frame period, and positive polarities again during an (n+1)th frame period. Because the common voltage of the liquid crystal panel 10 may shift slightly when the polarity of each pixel unit 130 is changed, the pixel units 130 displaying the same gray level but having opposite polarities may have different charging conditions. Accordingly, when the polarities of all the pixel units 130 in bright states displaying a same gray level are inverted at the same time, the corresponding image viewed by a user may flicker.
What is needed, therefore, is an LCD and a driving method for the LCD which can overcome the above-described deficiencies.